--> Geomechanical Analysis For De-Risking And Enhancing Production; Best Practices And Exa Oil & Gas Developments For Application To Geothermal Fields

AAPG European Region, Geothermal Cross Over Technology Workshop, Part II

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Geomechanical Analysis For De-Risking And Enhancing Production; Best Practices And Exa Oil & Gas Developments For Application To Geothermal Fields

Abstract

Geomechanics, in terms of subsurface modelling, is a relatively new discipline which involves the combined knowledge of stresses in the Earth, resulting from plate tectonics, as well as pore pressure and rock mechanical properties. Present day stress states strongly influence geothermal operations and they do in oil and gas fields. Geomechanical models are widely used in all stagesofoil and gasfield development or field re-purposing. During exploration and development, models are used to predict mud weights required for wellbore stability taking into account temperature and deviation effects as necessary. As fields turn to production, geomechanical models are used to understand the impacts of natural fractures on production, the potential of solids production, and the behaviour of hydraulic fractures. Geomechancial analysis are also used to understand oil and gas production or injection related risks. As acceptance in the subject of Geomechanics has grown, so has the technology needed for full integration between the Geophysics, Geology, Petrophysics, Reservoir Engineering and Geomechanics subsurface disciplines. Now, with the capability of coupling a geological model, with a reservoir flow simulation and a 3D geomechanical model, one is able to understand the effects of production and injection over the field life. With change in pressures through depletion or while re-injecting, there is a change in stress. Understanding this change is key to comprehending the risks to Casing, Caprock and Fault Integrity. The aim is to show that the geomechancial methods used in oil and gas applications are directly relatable to geothermal fields given the appropriate data and considerations. With such, the best practices for achieving an integrated subsurface solution to enhance and de-risk production are discussed through various examples. One example from a HPHT well will be used to highlight the effects of temperature on borehole stability and thus, the effects of mud weight required while drilling. As a wellbore heats up, from the time of drilling compared to logging and running casing, is it important to understand thermal effects to ensure no time dependent collapse will occur. Several examples, including one directly from a carbonate geothermal field and one from an underground gas storage application, will highlight geomechancial effects on natural fractures and faults. The cases show that these effects aid in the ability to define “sweet spots”, when accompanied by a 3D discrete fracture network assessment. In addition, by coupling the geomechancial model with the geological model and reservoir flow simulation, the examples show how injection and depletion pressures are optimized so that the critical limits to reduce risk of induced seismicity and/or caprock integrity issues are known.